Raman spectroscopy is a well-known method for investigating and determining a chemical composition of a sample, whether in solid, liquid or gaseous form. A fine laser, typically a single mode laser operating at a single wavelength, is directed at the sample. A scattered Raman signal is collected through an optical probe and analyzed in a high resolution spectrometer. The laser emits an input signal including photons at wavelength λi. The photons are scattered by the sample at a shifted wavelength λo dependent on the chemical composition of the sample, where λo>λi. The shift is a result of molecule-dependent-photons that cause some of the input energy to be absorbed by the sample before scattering. The scattered photons are unique for every molecule and thus the collected spectrum is a unique representation of the chemical composition of the sample.
Only a small portion of the input signal causes the Raman effect (on the order of 10−9 of the total input signal), so detection must be greatly enhanced. This results in the need for a high resolution and low noise spectrometer for detection. Such spectrometers are typically large in size, costly to acquire and operate, and require cooling which results in additional power consumption and additional costs. Recently, some handheld spectrometers have emerged, providing a size reduction, but at the expense of reduced spectral resolution, thereby limiting their usefulness.
Conventional spectrometers need to highly disperse light in order to reach sufficient resolution and, thus, are limited in functionality when miniaturized or designed as smaller devices. In a typical Raman spectroscopy device, the spectrometer accounts for more than 75% of the cost and a similar percentage of the size and weight of the device.